Vertical fin type bipolar junction transistor (BJT) device with a self-aligned base contact

A method of forming a silicon-germanium heterojunction bipolar transistor (HBT) device, comprising:

• forming a first doped semiconductor layer on a semiconductor substrate;
• forming a second doped semiconductor layer on the first doped semiconductor layer, wherein the material of the second doped semiconductor layer is silicon;
• forming a third doped semiconductor layer on the second doped semiconductor layer, wherein the material of the third doped semiconductor layer is silicon-germanium;
• forming a fourth doped semiconductor layer on the third doped semiconductor layer, wherein the material of the fourth doped semiconductor layer is silicon;
• forming a dummy emitter contact and contact spacers on the fourth doped semiconductor layer;
• removing portions of the first, second, third, and fourth semiconductor layers to form a vertical fin;
• recessing the second doped semiconductor layer and fourth doped semiconductor layer;
• depositing a condensation layer on the exposed surfaces of the second doped semiconductor layer, third doped semiconductor layer, and fourth doped semiconductor layer;
• reacting the condensation layer with the third doped semiconductor layer to form a protective segment on a condensed protruding portion of the third doped semiconductor layer;
• and
• removing the condensation layer from the second doped semiconductor layer and fourth doped semiconductor layer.